Geology & Mineralization
The Chandalar district is part of a regional Devonian-aged Ambler Schist belt that extends 600 miles east/west across Alaska along the southern flank of the Brooks Range. The geology is made up of sedimentary, volcanic and intrusive igneous rocks that have been variably metamorphosed, sheared and deformed. Both lode and placer gold mineralization occur throughout the district.
Lode gold deposits within the Chandalar district feature both sediment-hosted and orogenic-type, low-sulfidation gold mineralization. The most common occurrence of gold mineralization in the district is fault/joint-controlled, high-angle, mesothermal quartz veins. Primary structures are a set of west-northwest trending high-angle shear zones that cut Devonian-age or older greenschist-facies metamorphic rocks believed to be of the Coldfoot subterrane of the Arctic Alaska. Gold mineralization typically occurs as discontinuous quartz lenses and shear zone-controlled disseminations, stockwork, and sheeted veining.
Placers of the Chandalar district occur in fairly steep, second- and third-order streams that contain an abundance of locally derived sub-angular to sub-rounded clasts of schist, quartz, and greenstone dike rock. The mountain ridgeline that separates the placer stream basins averages about 5,000 feet in elevation, and there has been significant down cutting of a former highland lying south of Squaw Lake.
Placer gold deposits in the narrow, incised upper creek valleys occur in pay streaks under 10-to-35 feet of overburden. At distances of two-to-five miles below the heads of the valleys, placer gold exploration has found depth to bedrock to exceed 170 feet with pay streaks on bedrock surfaces.
The mineralization at Chandalar shares similar characteristics to many world-class deposits. These deposits are typically categorized as greenstone hosted, shear-zone, low-sulfide systems. These types of deposits account for a major part of the world's gold production and constitute one of the most common and sought-after types of deposits in Canada, Brazil, Australia, and other regions in the world.
These systems are typically associated with regional shear zones in metamorphic rock belts of varying lithology and age. They are thought to have formed at considerable depth in the earth's crust by hydrothermal and/or metamorphic processes.